1. Field of the Invention
The present invention relates to a method of purifying N-(2-hydroxyethyl)-2-pyrrolidone (herein HEP) by an improved distillation procedure which avoids separating HEP as an overhead distillate stream during the procedure.
2. Description of the Prior Art
HEP is an important chemical of commerce which is primarily useful for the production of N-vinyl-2-pyrrolidone by intermolecular dehydration, the N-vinyl-2-pyrrolidone having utility in the cosmetics, food additives and pharmaceutical industries.
An extensive description of the known procedures for producing and purifying HEP can be found in U.S. Pat. No. 6,726,811, the disclosure of which is incorporated herein in its entirety.
In the procedure described in U.S. Pat. No. 6,726,811, HEP of high purity is recovered from the reaction liquid resulting from reacting gamma-butyrolactone with 2-aminoethanol and which contains N-(2-hydroxyethyl)-2-pyrrolidone, low-boiling component and high-boiling component.
In the process of the reference, the reaction mixture is first distilled in column 1 to separate as overhead a lighter stream containing both light impurities and HEP from a heavier stream containing higher boiling components. The overhead stream from column 1 is then passed to one (FIG. 1) or two (FIG. 2) columns for ultimate recovery of purified HEP.
It has now been found that the distillation recovery of high purity HEP can be significantly enhanced by an improved distillation sequence as provided in accordance with the present invention.